Low-E matchable coated articles and methods of making same

ABSTRACT

A heat treatable coated article including an infrared (IR) reflecting layer (e.g., of or including Ag), the coated article being able to attain a ΔE* (glass side) no greater than about 3.0, more preferably no greater than 2.5, and even more preferably no greater than 2.0, following or due to heat treatment (e.g., thermal tempering). Accordingly, low-E (i.e., low emissivity) coated articles of certain embodiments of this invention appear from the glass side thereof visually similar to the naked eye both before and after heat treatment. Coated articles herein may be used in the context of insulating glass (IG) window units, vehicle windshields, or any other suitable applications. In certain embodiments of this invention, an exemplary layer stack includes: glass/Si 3 N 4 /NiCr/Ag/NiCr/Si 3 N 4 . Other materials may instead be used without departing from the scope and/or spirit of the instant invention which is a low-E matchable product.

This is a divisional of U.S. Ser. No. 10/310,854, filed Dec. 6, 2002(now U.S. Pat. No. 6,692,831), which is a continuation of U.S. Ser. No.10/246,746, filed Sep. 19, 2002 (now U.S. Pat. No. 6,558,800), which isa continuation of U.S. Ser. No. 09/793,404, filed Feb. 27, 2001 (nowU.S. Pat. No. 6,475,626), which is a continuation-in-part (CIP) ofcommonly owned U.S. patent application Ser. No. 09/455,026, filed Dec.6, 1999 now U.S. Pat. No. 6,514,620.

LOW-E MATCHABLE COATED ARTICLES AND METHODS OF MAKING SAME

This invention relates to low-E coated articles that have approximatelythe same color characteristics as viewed by the naked eye both beforeand after heat treatment (e.g., thermal tempering), and correspondingmethods. Such coated articles may be used in insulating glass (IG)units, windshields, and other suitable applications.

BACKGROUND OF THE INVENTION

Solar control coating systems are known. For example, commonly ownedU.S. Pat. No. 5,688,585 discloses a solar control coated articleincluding: glass/Si₃N₄/NiCr/Si₃N₄. One object of the '585 patent is toprovide a sputter coated layer system that after heat treatment ismatchable colorwise with its non-heat treated counterpart. While thecoating systems of the '585 patent are excellent for their intendedpurposes, they suffer from certain disadvantages. In particular, theytend to have rather high emissivity values (e.g., because no silver (Ag)layer is disclosed in the '585 patent).

Low-emissivity (low-E) coating systems are also known in the art. Forexample, commonly owned U.S. Pat. No. 5,376,455 discloses:glass/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄. Low-E coating systems such as this aretypically designed for maximum visible transmission. For this reason,the NiCr layers are made rather thin. This enables high transmission andlow-E characteristics, but less than desirable solar control (e.g.,shading coefficient) characteristics. Thus, the low-E coating system ofthe '455 patent is unfortunately not sufficiently color matchable afterheat treatment with its non-heat treated counterpart, and lacks superiorsolar control characteristics such as shading coefficient (SC).

Accordingly, when it is desired to provide an insulating glass (IG) unitwith both low emissivity (low-E) and solar control characteristics, ithas often been necessary to combine the solar control coating of the'585 patent with the low-E coating of the '455 patent in a single IGunit. For example, the solar control coating of the '585 patent isplaced on the #2 surface of the IG unit while the low-E coating of the'455 patent is placed on the #3 surface of the IG unit. The need forthese two separate and distinct coatings in an IG unit is undesirable,for cost, processing and/or performance reasons.

The need for matchability (before heat treatment vs. after heattreatment) is also known. Glass substrates are often produced in largequantities and cut to size in order to fulfill the needs of a particularsituation such as a new multi-window and door office building, vehiclewindshield needs, etc. It is often desirable in such applications thatsome of the windows and/or doors be heat treated (i.e., tempered, heatstrengthened or bent) while others need not be. Office buildings oftenemploy IG units and/or laminates for safety and/or thermal control. Itis desirable that the units and/or laminates which are heat treatedsubstantially match their non-heat treated counterparts (e.g., withretard to color, reflectance, and/or the like, at least on the glassside) for architectural and/or aesthetic purposes. In addition, it issometimes desirable that certain windows, doors, windshields, etc. be ofa substantially neutral color, preferably tending to the blue-green sideof the spectrum.

It has in the past been possible to achieve matchability in systemsother than those of the aforesaid '585 patent, but only between twodifferent layer systems, one of which is heat treated and the other isnot. The necessity of developing and using two different layer systemsto achieve matchability creates additional manufacturing expense andinventory needs which are undesirable.

U.S. Pat. Nos. 6,014,872 and 5,800,933 (see Example B) disclose a heattreatable low-E layer system including: glassTiO₂/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄. Unfortunately, when heat treated thislow-E layer system is not approximately matchable colorwise with itsnon-heat treated counterpart (as viewed from the glass side). This isbecause this low-E layer system has a ΔE* (glass side) value of greaterthan 4.1 (i.e., for Example B, Δa*_(G) is 1.49, Δb*_(G) is 3.81, and ΔL*(glass side) is not measured; using Equation (1) below then ΔE* on theglass side must necessarily be greater than 4.1 and is probably muchhigher than that).

In view of the above, it will be apparent to those skilled in the artthat there exists a need for a coating or layer system that couldsatisfy both solar control and low-E requirements (e.g., so a solarcontrol coating and a separate low-E coating need not be used togetheron different surfaces of the same IG unit). In addition to and/orinstead of the above need, there also exists a need in the art for alow-E coating or layer system which after heat treatment substantiallymatches in color and/or reflection (as viewed by a naked human eye fromthe glass side) its non-heat treated counterpart. In other words, thereexists a need in the art for a low-E matchable coating or layeringsystem.

It is a purpose of this invention to fulfill any and/or all of theabove-listed needs, and/or other needs which will become more apparentto the skilled artisan once given the following disclosure.

SUMMARY OF THE INVENTION

An object of this invention is to provide a low-E coating or layersystem that has good color stability with heat treatment.

Another object of this invention is to provide a low-E matchable coatingor layering system.

Another object of this invention is to provide a coating or layer systemthat has improved IR reflectance characteristics relative to those ofthe coating systems described in U.S. Pat. No. 5,688,585.

Another object of certain embodiments of this invention is to provideimproved solar control characteristics (e.g., low shading coefficientand/or visible transmittance) relative to those of the '455 patent.

Another object of this invention is to provide a coating or layer systemthat when heat treated is substantially matchable to its non-heattreated counterpart.

Another object of this invention is to fulfill one or more of theabove-listed objects.

It has been surprisingly found that silver in rather substantialthicknesses may be employed while still achieving color stability withheat treatment (e.g., thermal tempering, bending, or heatstrengthening). The layer systems of the invention may be utilized, forexample, in the context of IG units, vehicle windows and windshields, orthe like.

According to certain exemplary embodiments of this invention, one ormore of the above-listed objects or needs is/are fulfilled by providinga coated article comprising:

a layer system supported by a glass substrate, said layer systemcomprising an infrared (IR) reflecting silver layer located betweenfirst and second dielectric layers; and

wherein said coated article has a ΔE* value (glass side, reflectance) nogreater than 3.0 (more preferably no greater than 2.5) after or due toheat treatment.

Further embodiments of this invention fulfill one or more of theabove-listed needs or objects by providing a coated article comprising:

a substrate;

a layer system provided on the substrate, said layer system comprisingfrom the glass outwardly, a first silicon nitride inclusive layer, afirst Ni or NiCr inclusive layer, an IR reflecting metal layer, a secondNi or NiCr inclusive layer, and a second silicon nitride inclusivelayer;

wherein each of said first and second Ni or NiCr inclusive layers is atleast about 20 Å thick; and

wherein said coated article has a hemispherical emissivity (E_(h)) of nogreater than 0.25 before heat treatment, a sheet resistance R_(s) nogreater than 20 ohms/square before heat treatment, and a ΔE* value(glass side, reflectance) no greater than 2.5 after or due to heattreatment.

Other embodiments of this invention fulfill one or more of theabove-listed needs or objects by providing a method of making a coatedarticle, the method comprising:

depositing a layer system on a glass substrate, the layer systemincluding an infrared (IR) reflecting metal layer located between firstand second dielectric layers, wherein prior to heat treatment the glasssubstrate with the layer system thereon has a sheet resistance R_(s) nogreater than 20 ohms/square; and

heat treating the substrate with the layer system thereon so that due tosaid heat treating the resulting substrate with the layer system thereonhas a ΔE* value (glass side; reflectance) no greater than 2.5.

Other embodiments of this invention fulfill one or more of theabove-listed needs or objects by providing a an insulating glass (IG)window unit comprising:

first and second glass substrates sealed together proximate theirrespective peripheral edges so as to form an insulating spacetherebetween;

a layer system supported by one of said glass substrates proximate saidinsulating space, said layer system comprising an infrared (IR)reflecting silver layer located between first and second dielectriclayers; and

wherein said IG unit has a ΔE* value (exterior or outside) no greaterthan 3.0 after or due to heat treatment.

This invention will now be described with respect to certain embodimentsthereof as illustrated in the following drawings, wherein:

IN THE DRAWINGS

FIG. 1 is a partial side cross sectional view of an embodiment of alayer system according to this invention.

FIG. 2 is a partial cross-sectional view of an IG unit as contemplatedby this invention, in which the layer system of FIG. 1 may be used.

DETAILED DESCRIPTION OF CERTAIN EXEMPLARY EMBODIMENTS OF THE INVENTION

Certain embodiments of this invention provide a coating or layer systemthat may be used in applications such as IG units, vehicle windows,vehicle windshields, and other suitable applications. Certainembodiments of this invention provide a layer system that has excellentcolor stability (i.e., a low value of ΔE* and/or a low value of Δa*;where Δ is indicative of change in view of heat treatment) with heattreatment (e.g., thermal tempering, bending, or thermal heatstrengthening) both monolithically and in the context of dual paneenvironments such as IG units or windshields. Such heat treatments oftennecessitate heating the coated substrate to temperatures above 1100° F.(593° C.) and up to 1450° F. (788° C.) [more preferably from about 1100to 1200 degrees F.] for a sufficient period of time to insure the endresult (e.g., tempering, bending, and/or heat strengthening). Certainembodiments of this invention combine both (i) color stability with heattreatment, and (ii) the use of a silver layer for selective IRreflection. Certain embodiments of this invention combine (i) and (ii),along with (iii) color in the blue-green quadrant (i.e., third quadrant)of the color spectrum when applied to a clear and/or green glasssubstrate. Certain embodiments of this invention combine (i), (ii) and(iii), along with (iv) low-emissivity characteristics.

FIG. 1 is a side cross sectional view of a coated article according toan embodiment of this invention. The coated article includes substrate 1(e.g., clear, green, bronze, grey, blue, or blue-green glass substratefrom about 1.0 to 12.0 mm thick), first dielectric layer 3 (e.g., of orincluding silicon nitride (e.g., Si₃N₄), titanium dioxide, titaniumnitride, zirconium oxide, zirconium nitride, tin oxide, silicon oxide,silicon dioxide, silicon oxynitride, or zinc oxide), nickel (Ni) ornickel-chrome (NiCr) inclusive layer 5 (other oxidation resistantmaterials may be used instead of Ni or NiCr in alternative embodimentsof this invention), IR reflecting silver (Ag) inclusive layer 7, nickel(Ni) or nickel-chrome (NiCr) inclusive layer 9 (other oxidationresistant materials may be used instead of Ni or NiCr in alternativeembodiments of this invention), and second dielectric layer 11 (e.g., ofor including silicon nitride (e.g., Si₃N₄), titanium dioxide, titaniumnitride, zirconium nitride, zirconium oxide, tin oxide, silicon oxide,silicon dioxide, silicon oxynitride, or zinc oxide). Other layer(s)below or above the illustrated coating system may also be provided.Thus, while the layer system is “on” or “supported by” substrate 1(directly or indirectly), other layer(s) may be provided therebetween.Thus, for example, the layer system of FIG. 1 may be considered “on” thesubstrate 1 even though other layer(s) are provided therebetween.

IR reflecting Ag layer 7 is preferably Ag metal, although it is possiblethat some small amount of oxidation could occur with respect thereto.The same is true for Ni or NiCr layers 5 and 9. Thus, in certainpreferred embodiments of this invention, layers 5, 7 and 9 are no morethan about 25% oxidized, more preferably no more than about 10%oxidized, and most preferably no more than 1% oxidized. In certainpreferred embodiments, layers 5 and/or 9 are of non-nitrided andnonoxidized nickel or nickel alloy (e.g., nichrome of, by weightpercent, 80/20 nickel/chrome). An exemplary apparatus which may be usedto form the layer coating systems of this invention is a conventionalsputter coating system, such as the multichamber G-49 large area flatglass sputter coater produced by Airco, Inc.

In embodiments of this invention where layers 3 and 11 comprise Si₃N₄, atarget including Si employed to form these layers may be admixed with upto 6-20% by weight aluminum or stainless steel (e.g. SS#316), with aboutthis amount then appearing in the layers so formed. Moreover, whilelayers 5 and 9 may be metallic nickel, a nichrome preferably consistingessentially of, by weight about 80-90% Ni and 10-20% Cr, may be employedin certain preferred embodiments. Other metals or alloys may also beused in alternative embodiments, e.g., alloy(s) include 10% or more Ni.Moreover, while it is possible to employ certain other IR reflectingmetals as layer 7, such as gold or platinum in certain embodiments ofthis invention, layer 7 herein consists essentially of metallic silverin certain embodiments of this invention. An example of layers 5 and 9includes not only SS-316 which consists essentially of 10% Ni and 90%other ingredients, mainly Fe and Cr, but Haynes 214 alloy as well, whichby weight consists essentially of (as a nominal composition):

Element Weight % Ni 75.45 Fe 4.00 Cr 16.00 C .04 Al 4.50 Y .01

In other embodiments of this invention, coated articles may be asfollows: glass/siliconnitride/nichrome/silver/nichrome/silver/nichrome/silicon nitride. Insuch embodiments, the respective silicon nitride, nichrome and/or silverlayers may have thicknesses similar to those discussed for thesematerials in other embodiments of this invention. Alternatively, certainlayers may be thinner, for example as follows: glass/silicon nitride (40Å)/nichrome(35 Å)/silver(50 Å)/nichrome(30 Å)/silver(50 Å)/nichrome(35Å)/silicon nitride(261 Å). It is believed that these dual silverembodiments may experience improved color stability and/or chemicalresistance characteristics relative to the FIG. 1 embodiment asdescribed herein. This embodiment may even experience better durabilitythan the FIG. 1 embodiment in certain instances.

FIG. 2 illustrates the coating or layer system 22 of FIG. 1 (or of theaforesaid dual silver embodiment) being utilized on surface #2 of an IGwindow unit. In order to differentiate the “inside” of the IG unit fromits “outside”, the sun 19 is schematically presented on the outside. TheIG unit includes outside glass pane or sheet 21 and inside glass pane orsheet 23. These two glass substrates (e.g. float glass 2 mm to 2 mmthick) are sealed at their peripheral edges by a conventional sealant 25and are provided with a conventional desiccant strip 27. The panes arethen retained in a conventional window or door retaining frame (shown inpartial schematic form). By sealing the peripheral edges of the glasssheets and replacing the air in insulating space (or chamber) 30 with agas such as argon, a typical, high insulating value IG unit is formed.Optionally, insulating space 30 may be at a pressure less thanatmospheric pressure in certain alternative embodiments, although thisof course is not necessary in all embodiments. Either inner wall 24 or26 (or both) may be provided with a layer system (see FIG. 1) of thisinvention. In this illustrated embodiment of FIG. 2, inner wall 24(i.e., surface #2) of outside glass sheet 21 has been provided with asputter-coated layer system of FIG. 1 thereon.

Turning back to FIG. 1, while various thicknesses may be used consistentwith one or more of the objects and/or needs discussed herein, accordingto certain exemplary embodiments of this invention, the preferredthicknesses and materials for the respective layers on the glasssubstrate 1 are as follows:

TABLE 1 (Thicknesses) Layer Preferred Range () More Preferred () Si₃N₄(layer 3) 300-380 320-360 NiCr (layer 5) 20-150 20-90 Ag (layer 7)40-120 60-80 NiCr (layer 9) 20-150 20-90 Si₃N₄ (layer 11) 400-500420-480

As can be seen from Table 1 above, the upper Ni or NiCr layer 9 has beensubstantially thickened relative to embodiments of the aforesaid '455patent. Moreover, dielectric layer(s) 3 and/or 11 has/have been thinnedrelative to the '455 patent. Surprisingly, it is believed that one ormore of these changes results in the matchability or lower ΔE* values(to be described below) associated with certain embodiments of thisinvention (i.e., improved stability with heat treatment). One or both ofthese changes may also be associated with improved durabilityexperienced by certain embodiments of this invention. Also, it is notedthat these embodiments represent a significant improvement over the '585patent because the instant inventor has found a way to (i) use an Aglayer to reflect IR so as to achieve a low-E layer system, and at thesame time (ii) have good stability with heat treatment (i.e., a low ΔE*and/or Δa* value(s)). This combination of a low-E system with goodstability with heat treatment is believed novel and inventive.

In certain exemplary embodiments, the stability with heat treatmentresults in substantial matchability between heat treated and non-heattreated versions of the coating or layer system. In other words, inmonolithic and/or IG applications, in certain embodiments of thisinvention two glass substrates having the same coating system thereon(one heat treated after deposition and the other not heat treated)appear to the naked human eye to look substantially the same when viewedfrom the glass side of the product (i.e. looking through at least onesubstrate of glass before viewing the coating). In certain embodimentsof this invention it has also been found that matchability (whileachievable in monolithic applications) may even be improved in IG and/orlaminate applications.

Thus, in certain embodiments, matchability is achieved monolithically.However, other embodiments only achieve matchability when used in a dualor multi-glass substrate structure such as an IG unit. The matchabilityimprovement in an IG unit occurs due to moderating effect of the insideglass pane 26 (FIG. 2). Light reflected from the inside pane 26approximately adds up to the light reflected from the outside pane 21.Consequently, perceived IGU color in reflection is some weighted averageof colors reflected from the individual panes 21 and 26. The impact ofeach pane on the resulting color will stay in some proportion to thepercentage of light reflected from each pane and reaching viewers eye.Considering the outside observer, the light reflected from the outsidepane 21 will reach viewers eye without obstruction. However, the lightreflected from the inside pane 26 will have to go through the front panetwice (once before being reflected from the inside pane and once after)before reaching the same viewer's eye. In effect, the amount of lightreflected from the inside pane will be reduced by a factor equal to thesquared transmittance of the outside pane. For that reason, moderatingeffect of the inside pane will be diminishing quickly with decreasingvisible transmittance of the front pane 21. The diminishing effect willbe even greater due to the fact that, typically, the reflectance of thecoated pane 21 will be increasing as the transmittance decreases, thusfurther increasing the percentage of the light reflected from the frontpane in the light reflected from the IG unit. For example, the coatedproduct described in the mentioned patent application Ser. No.09/455,026 in the annealed state had visible transmittance about 70% andthe class side reflectance about 10%. The transmittance was increasingto about 75% while glass side reflectance was decreasing to about 8% forthe heat treated product. The total outside reflectance for the heattreated IG unit will be 8% from the front pane, and 8% (reflectance ofuncoated glass)*0.75²=4.5%. Thus, the light reflected from the insidepane 26 amounts to 36% of the total outside reflectance from the heattreated IG unit. That means, that the IG unit ΔE*_(IGU) will be reducedby about 36% as compared to the monolithic ΔE*_(mono). It has beendetermined (U.S. patent application Ser. No. 09/455,026, pages 39 and40) that due to about 5% transmittance increase during heat treatment,the actual moderating effect was even greater (about 55%, measuredΔE*_(mono)=3.95, ΔE*_(IGU)=1.76). In contrast, the moderating effect forthe lower transmittance coated products such as Example #2 of thispatent application, will be almost nonexistent. For the heat treated IGunit, the outside reflectance from the front pane 21 was 16.51%. Thetransmittance of the heat treated front pane was 44.91. The totaloutside reflectance from the IG unit as shown at FIG. 2 may becalculated as 16.51% from the front pane 21, and 8% * 0.45²=1.62% fromthe inside pane 26. In this case, the light from the inside pane 26 willbe only about 9% of the total IG unit reflectance and the expectedmoderating effect on ΔE* will be about 9%. The additional moderatingeffect due to transmittance increase in heat treatment will also be verysmall in this case since transmittance increase is very small(ΔT=0.72%). The consideration proves, that for the lower transmittancecoatings, to achieve matchability in an IG unit, the matchability mustbe practically achieved for the coated front pane 21 in the monolithicstate. Thus, in certain embodiments, generally these with transmittancehigher than 60%, the ΔE of the monolithic (individual) substrate may besubstantially higher than 2.5 and matchability still be achieved in thedual or multipane articles of this invention. However, in certain otherembodiments, generally those with transmittance lower than 60%, the ΔEof the monolithic (individual) substrate may not be substantially higherthan 2.5, preferably lower than 2.5, in order to achieve matchability inthe dual or multipane articles of this invention. In the Examples #1-4,ΔE* values are reduced by 0.5-0.8 points for the higher transmittancesamples (#1 and #3), and by 0.2-0.3 points for the lower transmittancesamples (#2 and #4).

The values ΔE* and Δa* are important in determining whether or not thereis matchability, or substantial matchability, in the context of thisinvention. Color herein is described by reference to the conventionala*, b* values, which in certain embodiments of this invention are bothnegative in order to provide color in the desired substantially neutralcolor range tending to the blue-green quadrant. The term Δa* is simplyindicative of how much color value a* changes due to heat treatment.

The term ΔE* (and ΔE) is well understood in the art and is reported,along with various techniques for determining it, in ASTM 2244-93 aswell as being reported in Hunter et. al., The Measurement of Appearance,2^(nd) Ed. Cptr. 9, page 162 et seq. [John Wiley & Sons, 1987]. As usedin the art, ΔE* (and ΔE) is a way of adequately expressing the change(or lack thereof) in reflectance and/or transmittance (and thus colorappearance, as well) in an article after or due to heat treatment. ΔEmay be calculated by the “ab” technique, or by the Hunter technique(designated by employing a subscript “H”). ΔE corresponds to tie HunterLab L, a, b scale (or L_(h), a_(h), b_(h)). Similarly, ΔE* correspondsto the CIE LAB Scale L*, a*, b*. Both are deemed useful, and equivalentfor the purposes of this invention. For example, as reported in Hunteret. al. referenced above, the rectangular coordinate/scale technique(CIE LAB 1976) known as the L*, a*, b* scale may be used,

wherein:

-   -   L* is (CIE 1976) lightness units    -   a* is (CIE 1976) red-green units    -   b* is (CIE 1976) yellow-blue units        and the distance ΔE* between L*_(o) a*_(o) b*_(o) and L*₁ a*₁        b*₁ is:        ΔE*=[(ΔL*)²+(Δa*)²+(Δb*)²]^(1/2)  (1)        where:        ΔL*=L*₁ −L*_(o)  (2)        Δa*=a*₁ −a*_(o)  (3)        Δb*=b*₁ −b*_(o)  (3)        where the subscript “0” represents the coating (coated article)        before heat treatment and the subscript “1” represents the        coating (coated article) after heat treatment; and the numbers        employed (e.g., a*, b*, L*) are those calculated by the        aforesaid (CIE LAB 1976) L*, a*, b* coordinate technique. In a        similar manner, ΔE may be calculated using equation (1) by        replacing a*, b*, L* with Hunter Lab values a_(h), b_(h), L_(h).        Also within the scope of this invention and the quantification        of ΔE* are the equivalent numbers if converted to those        calculated by any other technique employing the same concept of        ΔE* as defined above.

In certain embodiments of this invention, layer systems herein providedon clear monolithic glass substrates have color as follows before heattreatment, as viewed from the glass side of the coated article (R_(G)%):

TABLE 2 Color (R_(G)) Before Heat Treatment General Preferred a*   0.0to −5.0   0.0 to −3.0 b* −1.0 to −10.0 −3.0 to −9.0

After heat treatment, in certain embodiments of this invention layersystems provided on clear monolithic glass substrates have colorcharacteristics ΔE* and Δa* as follows, when viewed from the glass (G)side (as opposed to the layer side) of the coated article:

TABLE 3 Color Characteristics (ΔE*_(G) & Δa*_(G)) After Heat TreatmentGeneral Preferred ΔE*_(G) is <=3.0 <=2.5 (or <=2.0) Δa*_(G) is <=1.0<=0.8

Accordingly, as shown in Table 3 above, coated articles according tocertain embodiments of this invention have a ΔE* value (glass side) ofno greater than 3.0, more preferably no greater than 2.5, and even morepreferably no greater than 2.0; and have a Δa* value (glass side) of nogreater than about 1.0, more preferably no greater than 0.8. When one orboth of these are achieved, matchability may result. It is noted that b*values are not deemed as important as a* values, because a* changes arebelieved to be more noticeable to the naked human eye than are b*changes in certain instances.

EXAMPLES 1-4

The following four Example coated articles (each annealed and heattreated) were made in accordance with certain embodiments of thisinvention. For each of the four Examples, the layer system was:glass/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄ (e.g., see FIG. 1). For each of theseExamples, the substrate was of substantially clear 5.6-6.0 mm thicksoda-lime-silica glass. The coater/process setups for the four Exampleswere as follows.

With regard to Examples 1-2, they were made using a G-49 large area flatglass sputter coater produced-by Airco, Inc., using line speed of 170IPM, with coat zones 3-5 being used; where “*” means Al content ofapproximately 10% and gas (e.g., Ar, N₂) flow was measured in sccmunits. All targets for Examples 1-2 were C-Mag targets, except that thetargets used for depositing the Ag and NiCr layers (target #s 19-21)were planar. Moreover, in Examples 1-2 the first silicon nitride layerwas deposited in coat zone 3 using AC power, the NiCr and Ag layers weredeposited in coat zone 4 using DC power, and the overcoat siliconnitride layer was deposited in coat zone 5 using AC power. The coaterwas set up and ran as follows during the sputtering of Examples 1-2:

TABLE 4 Coater Setup/Processes for Examples 1-2 Voltage Pressure CathodeTarget Power (kW) (V) (mTorr) Ar flow N₂ flow EXAMPLE #1 #13 Si/Al* 27.7444 2.5 551 1489 #14 Si/Al* 27.7 451 2.5 551 1489 #15 Si/Al* 27.7 4592.5 551 1489 #16 Si/Al* 27.7 481 2.5 551 1489 #17 Si/Al* 27.7 453 2.5551 1489 #18 Si/Al* 27.7 480 2.5 551 1489 #19 NiCr 10.5 n/a 2.7 1110 0#20 Ag 4.15 n/a 2.7 1110 0 #21 NiCr 10.5 n/a 2.7 1110 0 #22 Si/Al* 33.6465 2.5 541 1336 #23 Si/Al* 33.6 462 2.5 541 1336 #24 Si/Al* 33.6 4522.5 541 1336 #25 Si/Al* 33.6 456 2.5 541 1336 #26 Si/Al* 33.6 478 2.5541 1336 #27 Si/Al* 33.6 463 2.5 541 1336 EXAMPLE #2 #13 Si/Al* 27.7 4442.5 551 1489 #14 Si/Al* 27.7 451 2.5 551 1489 #15 Si/Al* 27.7 459 2.5551 1489 #16 Si/Al* 27.7 481 2.5 551 1489 #17 Si/Al* 27.7 453 2.5 5511489 #18 Si/Al* 27.7 480 2.5 551 1489 #19 NiCr 17.0 n/a 2.7 1110 0 #20Ag 4.15 n/a 2.7 1110 0 #21 NiCr 17.0 n/a 2.7 1110 0 #22 Si/Al* 33.6 4652.5 541 1336 #23 Si/Al* 33.6 462 2.5 541 1336 #24 Si/Al* 33.6 452 2.5541 1336 #25 Si/Al* 33.6 456 2.5 541 1336 #26 Si/Al* 33.6 478 2.5 5411336 #27 Si/Al* 33.6 463 2.5 541 1336

Examples 3-4 were made using a Leybold TG-1 sputter coater using linespeed of 4 m/min.; where “*” again means aluminum (Al) target content ofapproximately 10% and gas (e.g., Ar, N₂) flow was measured in sccmunits. Target #s 34, 42, 55 and 61 were 2×C-Mag targets, target #'s 44,51 and 53 were planar targets, and target #65 was a Twin-Mag target.Pressure was measured in mTorr. The coater was set up and ran as followsduring the sputtering of Examples 3-4:

TABLE 5 Coater Setup/Processes for Examples 3-4 Power Voltage Freq.Cathode Target (kW) (V) Pressure Ar flow N₂ flow (kHz) EXAMPLE #3 #34Si/Al* 64.5 395 3.6 203 452 28.1 #42 Si/Al* 64.5 341 3.1 200 452 28.7#44 NiCr 12.5 385 2.5 220 0 DC #51 Ag 4.55 466 2.3 315 0 DC #53 NiCr12.5 421 2.4 220 0 DC #55 Si/Al* 62 373 3.5 200 447 27.8 #61 Si/Al* 64374 4.5 200 447 28.1 #65 Si/Al* 62 326 3.5 200 377 27.8 EXAMPLE #4 #34Si/Al* 64.5 395 3.6 203 452 28.1 #42 Si/Al* 64.5 341 3.1 200 452 28.7#44 NiCr 19 347 2.5 220 0 DC #51 Ag 4.55 466 2.3 315 0 DC #53 NiCr 19379 2.4 220 0 DC #55 Si/Al* 62 373 3.5 200 447 27.8 #61 Si/Al* 64 3744.5 200 447 28.1 #65 Si/Al* 62 326 3.5 200 377 27.8

After being sputtered onto a glass substrate as set forth above,Examples 1-4 were tested and were found to have the followingcharacteristics monolithically (not in a IG unit), where the heattreatment was thermally tempering the monolithic product in aconventional tempering furnace at approximately 1265° F. for threeminute cycles and quenching to room temperature (note: a* and b* colorcoordinate values are in accordance with CIE LAB 1976, Ill. CIE-C 2degree observer technique):

TABLE 6 Characteristics of Examples 1-4 (Monolithic) BeforeValue/Measurement Heat Treatment After Heat Treatment EXAMPLE #1Transmission (TY) %: 56.36 59.21 L*_(T): 79.82 81.41 a*_(T): −3.14 −3.27b*_(T): −3.93 −4.68 Reflectance as viewed from 12.68 11.52 glass (G)side: R_(G)Y (%): L*_(G): 42.27 40.44 a*_(G): −1.95 −1.53 b*_(G): −6.72−7.06 ΔE* (i.e., from glass (G) side): 1.9 Δa*_(G) (absolute value):0.42 Reflectance as viewed from 2.71 2.78 film/coating (F) side: R_(F)Y(%): L*_(F): 18.86 19.12 a*_(F): 11.58 12.73 b*_(F): 0.28 −1.59 R_(S)(sheet resistance in ohms/sq.) 12.0 10.8 Total Solar T %: 38 SolarR_(out): 16 U Value: 0.74 U Value S: 0.69 Shading Coefficient (SC): 0.54SHGC: 0.463 Heat Gain: 117 E_(h) (hemispherical emissivity): 0.176EXAMPLE #2 Transmission (TY) %: 44.19 44.91 L*_(T): 72.36 72.83 a*_(T):−3.68 −3.2 b*_(T): −5.82 −6.3 Reflectance as viewed from 17.05 16.51glass (G) side: R_(G)Y (%): L*_(G): 48.33 47.64 a*_(G): −1.26 −1.37b*_(G): −3.09 −3.37 ΔE* (i.e., glass (G) side): 0.8 Δa*_(G) (absolutevalue): 0.11 Reflectance as viewed from 4.6 4.63 film/coating (F) side:R_(F)Y (%): L*_(F): 25.55 25.66 a*_(F): 15.09 13.7 b*_(F): 11.73 14.62R_(s) (sheet resistance in ohms/sq.) 11.3 10.6 Total Solar T %: 29 SolarR_(out): 20 U Value: 0.74 U Value S: 0.70 Shading Coefficient (SC): 0.45SHGC: 0.385 Heat Gain: 99 E_(h) (hemispherical emissivity): 0.169EXAMPLE #3 Transmission (TY) %: 56.98 58.71 L*_(T): 80.17 81.13 a*_(T):−2.82 −2.82 b*_(T): −2.23 −2.73 Reflectance as viewed from 15.27 14.21glass (G) side: R_(G)Y (%): L*_(G): 46 44.53 a*_(G): −2.17 −1.81 b*_(G):−8.63 −8.95 ΔE* (glass (G) side): 1.5 Δa*_(G) (absolute value): 0.36Reflectance as viewed from 2.19 2.32 film/coating (F) side: R_(F)Y (%):L*_(F): 16.47 17.1 a*_(F): 13.68 13.76 b*_(F): −14.48 −13.25 R_(s)(sheet resistance in ohms/sq.) 11.5 10.5 Total Solar T %: 39 SolarR_(out): 19 U Value: 0.74 U Value S: 0.68 Shading Coefficient (SC): 0.55SHGC: 0.47 Heat Gain: 119 E_(h) (hemispherical emissivity): 0.170EXAMPLE #4 Transmission (TY) %: 50.08 51.08 L*_(T): 76.12 76.73 a*_(T):−3.61 −2.88 b*_(T): −5.02 −4.66 Reflectance as viewed from 14.62 13.82glass (G) side: R_(G)Y (%): L*_(G): 45.1 43.98 a*_(G): −0.59 −1.36b*_(G): −4.33 −4.52 ΔE* (glass (G) side): 1.4 Δa*_(G) (absolute value):0.77 Reflectance as viewed from 3.83 3.67 film/coating (F) side: R_(F)Y(%): L*_(F): 23.09 22.56 a*_(F): 15.93 11.79 b*_(F): 3.51 10.42 R_(s)(sheet resistance in ohms/sq.) 11.0 9.1 Total Solar T %: 33 SolarR_(out): 19 U Value: 0.73 U Value S: 0.69 Shading Coefficient (SC): 0.49SHGC: 0.42 Heat Gain: 107 E_(h) (hemispherical emissivity): 0.164Moreover, each of Examples 1-4 was found to be chemically andmechanically durable as these terms are defined below, both before andafter heat treatment.

As can be seen from the above, each of Examples 1-4 had goodmatchability because, as viewed from the glass (G) side of therespective articles, ΔE* was no greater than 2.5, and preferably nogreater than 2.0; while Δa*_(G) (the absolute value thereof, as usedherein) was no greater than 1.0, and preferably no greater than 0.8.These values (i.e., ΔE* and Δa*) are important as measured from theglass (G) side of the coated article, as opposed to the film (F) sidebecause viewers in most applications predominantly view the productsfrom the glass sides thereof. With regard to matchability for example.Example 3 had the following values (viewed from the glass (G) side):

-   -   L* (before HT): 46; L* (after HT): 44.53; ΔL*=1.47    -   a* (before HT): −2.17; a* (after HT): −1.81 Δa*=0.36    -   b* (before HT): −8.63; b* (after HT): −8.95 Δb*=0.32

Thus, using the equation ΔE* =[(ΔL*)²+(Δa*)² +(Δb*)²]^(1/2), (i.e.,equation (1) above), it can be determined that[(1.47)²+(0.36)²+(0.32)²]^(1/2) =(2.3929)^(1/2)=1.5=ΔE* (glass side).This relatively low glass side reflectance ΔE* value indicates goodmatchability (before versus after heat treatment).

Each of the above-listed monolithic examples also had low-emissivitycharacteristics as shown by each of the above-listed Examples having ahemispherical emissivity (E_(h)) no greater than 0.25, and morepreferably no greater than 0.20, before and/or after heat treatment(HT). Thicker Ag layers may also be used, which would provide loweremissivity and/or sheet resistance than those report here, in accordancewith certain embodiments of this invention. Compare these low emissivityvalues to the hemispherical emissivity values of 0.48 to 0.73 in U.S.Pat. No. 5,688,585. Each of the aforesaid Examples 1-4 was alsocharacterized by low sheet resistance values of R_(s) no greater than 20ohms/square, more preferably no greater than 15 ohms/square, and evenmore preferably no greater than about 12 ohms/square (before and/orafter HT). Again, compare these low sheet resistance (R_(s)) values tothe sheet resistance values of 89-269 ohms/square in U.S. Pat. No.5,688,585. Accordingly, it can be seen that Examples 1-4 herein trulyhave low-E characteristics while at the same time surprisingly beingable to achieve substantial matchability before versus after heattreatment.

Monolithic coated articles according to certain embodiments of thisinvention preferably have a visible transmittance (TY %) of no greaterthan about 60%, more preferably from about 40-60% before HT, and mostpreferably from about 48-58% before HT. Monolithic coated articlesaccording to certain embodiments of this invention preferably have avisible transmittance (TY %) of from about 10-65% after HT, morepreferably from about 40-60% after HT. In a similar manner, coatedarticles according to certain embodiments of this invention preferablyhave a shading coefficient (SC) of no greater than about 0.65 (beforeand/or after HT), more preferably from about 0.40 to 0.60 (before and/orafter HT). Additionally, monolithic coated articles according to certainembodiments of this invention preferably have a glass side reflectancevalue (R_(G) Y %) of at least 11%, and more preferably from 12-20%before HT and from about 11-19% after HT.

It can also be seen that according to certain preferred embodiments ofthis invention monolithic coated articles are characterized by an a*_(G)value of from about 0.0 to −5.0, more preferably from about 0.0 to −2.5,before and/or after heat treatment. This enables coated articlesaccording to certain embodiments of this invention to have a desirableneutral or blue-green color, especially when b*_(G) is also negative.

The aforesaid characteristics may be measured at a clear float glassnominal substrate thickness of about 6 mm, or any other suitablesubstrate thickness from 1-12 mm. Moreover, it is noted that the unitsof Examples 1-4 may ultimately be utilized in the context of an IG unit,a windshield, window or the like.

Each of the aforesaid HT Examples 1-4 was then used in an IG unit asshown in FIG. 2 (e.g., where the insulating chamber or space between thetwo glass sheets may be filled with a gas such as Ar), with measurementsfrom these IG uses set forth below in Tables 7 and 8:

TABLE 7 Characteristics of Examples 1-4 (IG or IGU) (IG Unit as shown atthe FIG. 2. pane 26 - uncoated 6 mm clear glass) Before AfterValue/Measurement Heat Treatment Heat Treatment EXAMPLE #1 Transmission(TY) %: 50.17 52.52 L*_(T): 76.17 77.59 a*_(T): −4.54 −4.67 b*_(T):−3.54 −4.08 Reflectance as viewed from 15.15 14.45 outside (out) side:R_(out)Y (%): L*_(out): 45.84 44.87 a*_(out): −2.44 −1.76 b*_(out):−6.66 −7.15 ΔE*_(out) (from glass (out) side): 1.34 Δa*_(out) (absolutevalue): 0.68 Reflectance as viewed from 9.81 9.82 film/coating (inside)side: R_(in)Y (%): L*_(in): 37.51 37.51 a*_(in): 3.01 3.46 b*_(in):−0.48 −1.84 Total Solar T %: 31 Solar R_(out): 18 U Value: 0.34 U ValueS: 0.37 Shading Coefficient (SC): 0.43 TY %/SC 116.7 SHGC: 0.39 HeatGain: 96 EXAMPLE #2 Transmission (TY) %: 39.47 40.16 L*_(T): 69.09 69.58a*_(T): −4.95 −4.51 b*_(T): −4.97 −5.45 Reflectance as viewed from 18.8618.48 outside (out) side: R_(out)Y (%): L*_(out): 50.53 50.07 a*_(out):−1.82 −1.92 b*_(out): −3.57 −3.96 ΔE*_(out) (from glass (out) side):0.54 Δa*_(out) (absolute value): 0.1 Reflectance as viewed from 11.1111.04 film/coating (inside) side: R_(in)Y (%): L*_(in): 39.77 39.65a*_(in): 5.77 5.32 b*_(in): 3.03 3.50 Total Solar T %: 24 Solar R_(out):21 U Value: 0.34 U Value S: 0.36 Shading Coefficient (SC): 0.36 TY %/SC109.6 SHGC: 0.31 Heat Gain: 78 EXAMPLE #3 Transmission (TY) %: 50.5051.84 L*_(T): 76.37 77.18 a*_(T): −4.21 −4.19 b*_(T): −1.94 −2.34Reflectance as viewed from 17.93 17.35 outside (out) side: R_(out)Y (%):L*_(out): 49.41 48.69 a*_(out): −2.68 −2.58 b*_(out): −8.14 −8.44ΔE*_(out) (from glass (out) side): 0.70 Δa*_(out) (absolute value): 0.1Reflectance as viewed from 9.47 9.52 film/coating (inside) side: R_(in)Y(%): L*_(in): 36.87 36.97 a*_(in): 3.21 3.39 b*_(in): −5.91 −5.83 TotalSolar T %: 32 Solar R_(out): 20 U Value: 0.34 U Value S: 0.36 ShadingCoefficient (SC): 0.46 TY %/SC 109.8 SHGC: 0.4 Heat Gain: 97 EXAMPLE #4Transmission (TY) %: 44.41 45.60 L*_(T): 72.50 73.28 a*_(T): −4.91 −4.28b*_(T): −4.37 −4.18 Reflectance as viewed from 16.84 16.04 outside (out)side: R_(out)Y (%): L*_(out): 48.05 47.02 a*_(out): −1.31 −1.87b*_(out): −4.81 −4.97 ΔE*_(out) (from glass (out) side): 1.18 Δa*_(out)(absolute value): 0.56 Reflectance as viewed from 10.57 10.47film/coating (inside) side: R_(in)Y (%): L*_(in): 38.86 38.67 a*_(in):5.70 3.75 b*_(in): −0.05 2.59 Total Solar T %: 27 Solar R_(out): 20 UValue: 0.34 U Value S: 0.36 Shading Coefficient (SC): 0.4 TY %/SC 111SHGC: 0.35 Heat Gain: 86

For each of Examples 1-4, it can be seen from the Tables above that ΔE*improved when used in the context of an IG unit (e.g., see FIG. 2). Forproducts with higher visible transmittance (e.g., Examples 1 and 3), theΔE* improvement (i.e., ΔE* improvement may be characterized byΔE*_(mono)−ΔE*_(IG)) is was slightly better than the ΔE* improvement forthe lower visible transmittance examples (e.g., Examples 2 and 4). Asshown in Table 8 below, the ΔE* improvements (i.e., ΔE*_(mono)−ΔE*_(IG))for Examples 1-4 were 0.57, 0.21, 0.85, and 0.19, respectively. It isnoted that for Table 8 below, the reflective glass side ΔE* value forthe IG versions of Examples 1-4 was measured twice (2) with a Hunter LabUltraScan XE Spectrophotometer, the two measurements illustrating, forexample. instrument inaccuracy.

TABLE 8 ΔE* for Examples 1-4 (Mono vs. IG) Ex. #1 Ex. #2 Ex. #3 Ex. #4Measurement Monolithic Ex. #1 IG Monolithic Ex. #2 IG Monolithic Ex. #3IG Monolithic Ex. #4 IG T vis (%) 56.36 44.19 56.98 50.08 ΔE*_(g) 1.91.34 0.8 0.54 1.5 0.70 1.4 1.18 Δa* g 0.42 0.68 0.11 0.10 0.36 0.10 0.770.56 ΔE* g (2) 1.87 0.59 1.33 1.49 Δa* g (2) 0.80 0.17 0.21 0.67ΔE*_(mono) − ΔE*_(IGU) 0.57 0.21 0.85 0.19 ΔE*_((2)mono) − ΔE*_(IGU)0.53 0.05 0.63 0.31 ΔE* % improvement 29.8 28.3 54.7 14.0 (2) Repeatedmeasurement showing instrument accuracy

As can be seen from the above in Tables 7 and 8, in the context of an IGunit as shown in FIG. 2, each of the coatings of Examples 1-4 had goodmatchability because, as viewed from the outside of the respectivearticles (e.g., outside of a structure such as a building in which theIG unit is installed), ΔE* was no greater than 3.0, more preferably nogreater than 2.5, and even more preferably no greater than 2.0, and mostpreferably no greater than about 1.5 (e.g., for Example 1, ΔE* (outsidereflectance) in an IG unit was measured at 1.34, for Example 2 it was0.54, for Example 3 it was 0.70, and for Example 4 it was 1.18); whileΔa*_(outside) (the absolute value thereof, as used herein) was nogreater than 1.0, and preferably no greater than 0.8. These values(i.e., ΔE* and Δa*) are important as measured from theoutside/exterior/glass (G) side of the coated article (outside of theFIG. 2 structure), because viewers in most applications predominantlyview the products from e.g., outside of the building in which the IGunit is installed.

Each of the above-listed IG units had low-emissivity and sheetresistance characteristics as discussed above relative to monolithicembodiments. IG units according to certain embodiments of this inventionpreferably have a visible transmittance (TY %) of no greater than about60%, more preferably from about 30-60% before HT, and most preferablyfrom about 35-55% before HT. IG coated articles according to certainembodiments of this invention preferably have a visible transmittance(TY %) of from about 10-55% after HT, more preferably from about 35-55%after HT. In a similar manner, coated articles according to IGembodiments of this invention preferably have a shading coefficient (SC)of no greater than about 0.50 (before and/or after HT), more preferablyfrom about 0.25 to 0.47 (before and/or after HT). Additionally, IGcoated articles (e.g., FIG. 2) according to certain embodiments of thisinvention preferably have a glass side reflectance value (R_(G)Y %) offrom about 10-22% before HT and/or after HT.

It can also be seen that according to certain preferred embodiments ofthis invention IG embodiments are characterized by an a*_(G) (equivalentto a*_(out), value of from about 0.0 to −5.0, more preferably from about0.0 to −3.0, before and/or after heat treatment. This enables coatedarticles according to certain embodiments of this invention to have adesirable neutral or blue-green color, especially when b*_(G) is alsonegative.

Finally, in certain preferred IG embodiments of this invention the ratioof visible transmission (TY %) to shading coefficient (SC) (i.e., TY%/SC) is preferably no greater than 125.0, more preferably from about 90to 125, and most preferably from about 100 to 120. In certain IGembodiments, this is combined with a total solar transmittance of fromabout 20-34%, more preferably from about 24-33%.

Certain terms are prevalently used in the glass coating art,particularly when defining the properties and solar managementcharacteristics of coated glass. Such terms are used herein inaccordance with their well known meaning. For example, as used herein:

Intensity of reflected visible wavelength light, i.e. “reflectance” isdefined by its percentage and is reported as R_(x) Y or R_(x) (i.e. theY value cited below in ASTM E-308-85), wherein “X” is either “G” forglass side or “F” for film side. “Glass side” (e.g. “G”) means, asviewed from the side of the glass substrate opposite that on which thecoating resides, while “film side” (i.e. “F”) means, as viewed from theside of the glass substrate on which the coating resides.

Color characteristics are measured and reported herein using the CIE LABa*, b* coordinates and scale (i.e. the CIE a*b* diagram, III. CIE-C, 2degree observer). Other similar coordinates may be equivalently usedsuch as by the subscript “h” to signify the conventional use of theHunter Lab Scale, or Ill. CIE-C, 10° observer, or the CIE LUV u*v*coordinates. These scales are defined herein according to ASTM D-2244-93“Standard Test Method for Calculation of Color Differences FromInstrumentally Measured Color Coordinates” Sep. 15, 1993 as augmented byASTM E-308-85, Annual Book of ASTM Standards, Vol. 06.01 “StandardMethod for Computing the Colors of Objects by 10 Using the CIE System”and/or as reported in IES LIGHTING HANDBOOK 1981 Reference Volume.

The terms “emittance” and “transmittance” are well understood in the artand are used herein according to their well known meaning. Thus, forexample, the term “transmittance” herein means solar transmittance,which is made up of visible light transmittance (TY), infrared radiationtransmittance, and ultraviolet radiation transmittance. Total solarenergy transmittance (TS) is then usually characterized as a weightedaverage of these other values. With respect to these transmittances,visible transmittance, as reported herein, is characterized by thestandard CIE Illuminant C, 2 degree observer, technique at 380-720 nm;near-infrared is 720-2500 nm; ultraviolet is 300-800 nm; and total solaris 300-2500 nm. For purposes of emittance, however, a particularinfrared range (i.e. 2,500-40,000 nm) is employed.

Visible transmittance can be measured using known, conventionaltechniques. For example, by using a spectrophotometer, such as a PerkinElmer Lambda 900 or Hitachi U4001, a spectral curve of transmission isobtained. Visible transmission is then calculated using the aforesaidASTM 308/2244-93 methodology. A lesser number of wavelength points maybe employed than prescribed, if desired. Another technique for measuringvisible transmittance is to employ a spectrometer such as a commerciallyavailable Spectrogard spectrophotometer manufactured by PacificScientific Corporation. This device measures and reports visibletransmittance directly. As reported and measured herein, visibletransmittance (i.e. the Y value in the CIE tristimulus system, ASTME-308-85) uses the Ill. C.,2 degree observer.

“Emittance” (E) is a measure, or characteristic of both absorption andreflectance of light at given wavelengths. When transmittance is zero,which is approximately the case for float glass with wavelengths longerthan 2500 nm, the emittance may be represented by the formula:E=1−Reflectance_(film)

For architectural purposes, emittance values become quite important inthe so-called “mid-range”, sometimes also called the “far range” of theinfrared spectrum, i.e. about 2,500-40,000 nm., for example, asspecified by the WINDOW 4.1 program, LBL-35298 (1994) by LawrenceBerkeley Laboratories, as referenced below. The term “emittance” as usedherein, is thus used to refer to emittance values measured in thisinfrared range as specified by ASTM Standard E 1585-93 for measuringinfrared energy to calculate emittance, entitled “Standard Test Methodfor Measuring and Calculating Emittance of Architectural Flat GlassProducts Using Radiometric Measurements”. This Standard, and itsprovisions, are incorporated herein by reference. In this Standardemittance is reported as hemispherical emittance (E_(h)) and normalemittance (E_(n)).

The actual accumulation of data for measurement of such emittance valuesis conventional and may be done by using, for example, a Beckman Model4260 spectrophotometer with “VW” attachment (Beckman Scientific Inst.Corp.). This spectrophotometer measures reflectance versus wavelength,and from this, emittance is calculated using the aforesaid ASTM E1585-93 which has been incorporated herein by reference.

Another term employed herein is “sheet resistance”. Sheet resistance(R_(s)) is a well known term in the art and is used herein in accordancewith its well known meaning. It is here reported in ohms per squareunits. Generally speaking, this term refers to the resistance in ohmsfor any square of a layer system on a glass substrate to an electriccurrent passed through the layer system. Sheet resistance is anindication of how well the layer or layer system is reflecting infraredenergy, and is thus often used alone with emittance as a measure of thischaracteristic. “Sheet resistance” may for example be convenientlymeasured by using a 4-point probe ohmmeter, such as a dispensable4-point resistivity probe with a Magnetron Instruments Corp. head, ModelM-800 produced by Signatone Corp. of Santa Clara, Calif.

“Chemical durability” or “chemically durable” is used hereinsynonymously with the term of art “chemically resistant” or “chemicalstability”. Chemical durability is determined by boiling a 2″×5″ sampleof a coated glass substrate in about 500 cc of 5% HCl for one hour (i.e.at about 220° F.). The sample is deemed to pass this test (and thus thelayer system is “chemically resistant” or is deemed to be “chemicallydurable” or to have “chemical durability”) if the sample's layer systemshows no visible discoloration or visible peeling, and no pinholesgreater than about 0.003″ in diameter after this one hour boil.

“Mechanical durabilility” as used herein is defined by the followingtests. The test uses a Pacific Scientific Abrasion Tester (orequivalent) wherein a 2″×4″×1″ nylon brush is cyclically passed over thelayer system in 500 cycles employing 150 gm of weight, applied to a6″×17″ sample. In this test, if no substantial, noticeable scratchesappear when viewed with the naked eye under visible light, the test isdeemed passed, and the article is said to be “mechanically durable” orto have “mechanical durability”.

The terms “heat treatment” and “heat treating” as used herein meanheating the article to a temperature sufficient to enabling thermaltempering, bending, or heat strengthening of the glass inclusivearticle. This definition includes, for example, heating a coated articleto a temperature of at least about 1100 degrees F. (e.g., to atemperature of from about 550 degrees C. to 900 degrees C.) for asufficient period to enable tempering.

The term “U-value” or “U-Factor” (synonymous with “thermaltransmittance”) is a term well understood in the art and is used hereinaccording to this well known meaning “U-value” herein is reported interms of BTU/hr/ft²/degrees F., and may be determined according to theguarded hot box method as reported in, and according to ASTMdesignation: C1199-91.

The term “shading coefficient” is a term well understood in the art andis used herein according to its well known meaning. It is determinedaccording to ASHRAE Standard 142 “Standard Method for Determining andExpressing the Heat Transfer and Total Optical Properties ofFenestration Products” by ASHRAE Standards Project Committee, SPC 142,September 1995.

Once given the above disclosure many other features, modifications andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications and improvements are therefore considered to bea part of this invention, the scope of which is to be determined by thefollowing claims:

1. A method of making a heat treated coated article, the methodcomprising: providing a glass substrate; forming a multi-layer coatingon the glass substrate, the multi-layer coating having a sheetresistance of no greater than 20 ohms/square, and wherein the coatingcomprises at least one layer comprising silver sandwiched between atleast first and second dielectric layers; and heat treating the glasssubstrate with the multi-layer coating thereon so that the heat treatedcoated article has a glass side ΔE* value of no greater than 2.5.
 2. Themethod of claim 1, wherein the heat treated coated article has a glassside ΔE* value of no greater than 2.0.
 3. The method of claim 1, whereinthe heat treated coated article has a glass side Δa* value of no greaterthan 0.8.
 4. The method of claim 1, wherein at least one of thedielectric layers comprises silicon nitride which optionally may bedoped with aluminum.
 5. The method of claim 1, wherein a layercomprising NiCr is located immediately adjacent and contacting at leastone side of the layer comprising silver.
 6. The method of claim 1,wherein the heat treated coated article comprises an IG window unit.